Method of recovering thorium



2,815,122 Patented Dec. 10, 1957 ike METHOD OF RECOVERING THORIUM Ray W.Fisher, Ames, Iowa, assignor to the United States of America asrepresented by the United States Atomic Energy Commission No Drawing.Application March 4, 1948,

Serial No. 13,089

3 Claims. (Cl. 260-4291) This invention relates to a method ofrecovering thorium from a composition containing it. More specificallyit relates to a method of recovering thorium from slag material formedduring the reduction of salts of thorium to yield metallic thorium.

When thorium halides are treated at an elevated temperature with a metalselected from the group comprising alkali and alkaline earth metals,thorium is reduced to metallic form and a slag comprising a halide ofthe alkali or alkaline earth metal is produced. As shown in copendingapplication filed November 14, 1945, Serial No. 628,652, this process isbest carried out at a temperature above the melting point of thoriummetal. To secure this result the charge is heated sufliciently to startthe reaction and the heat formed by the reaction is augmented by theaddition of a booster. A suitable booster is iodine. An improvement inthis process is disclosed in copending application filed September 6,1946, Serial No. 695,299 and granted as U. S. Patent No. 2,782,116 onFebruary 19, 1957. According to this latter invention, the process ofproducing massive thorium metal is made easier by co-reducing a halideof Zinc or lead with the thorium halide. By either of these processes aslag is formed that contains mixed halides having a lower melting pointthan a slag comprising a simple halide, as for example, calciumfluoride.

Slags produced by the processes outlined above may contain variousmaterials including compounds of thorium which have not been reduced tometallic form. Thus a slag produced by co-reducing thorium tetrafluorideand zinc chloride using calcium metal in a ferrous metal containerhaving a lime liner was found to contain calcium, calcium oxide, thoriumoxide, iron, zinc fluoride, calcium fluoride, zinc metal, thorium metaland unreduced thorium tetrafluoride.

It is an object of this invention to provide a method of recoveringthorium from such a slag.

According to this invention the slag containing thorium is first leachedwith water to remove soluble salts such as calcium hydroxide. Theleachings are discarded and the residue is treated with concentratedhydrochloric acid which dissolves all free thorium metal, thoriumhydroxide, iron, calcium oxide and zinc salts. The material that isinsoluble in the acid comprises calcium fluoride, thorium fluoride, andthorium oxide.

The acid solution is made 1 to 3 normal in hydrochloric acid and thethorium is precipitated as the oxalate by the addition of oxalic acid.Preferably, a small amount of nitric acid is added to prevent theco-precipitation of ferrous oxalate.

The material insoluble in hydrochloric acid is digested in a watersolution of sodium hydroxide by gentle boiling for about four hours. Theresulting solution is diluted and filtered and the filtrate isdiscarded. The residue is treated with hydrochloric acid. Any residueleft after this latter treatment is again treated with sodium hydroxidesolution and hydrochloric acid as just shown. The combined acid-treatedsolution is made 1 to 3 normal in hydrochloric acid and the thorium isprecipitated by the addition of oxalic acid.

The operation oi this invention is illustrated by the following example:

Example 1 Step 1.-A sample of slag weighing one kilogram was preparedfor treatment by grinding. The ground sample was then leached with oneliter of water. In this treatment heat was produced and hydrogen andacetylene gases were evolved, the resulting solution being then in theform of a thick slurry.

Step 2.The residue from the water leach, containing about 1220 grams ofmaterial on a dry basis, was then treated with 3.3 liters (7.32 pounds)of concentrated hydrochloric acid. The resulting solution was filtered.The acidity of the filtrate was 1-3 normal. Then 10 milliliters ofconcentrated nitric acid were added. Next 70 grams of oxalic acid excessof the stoichiometric amount) were added and the solution was allowed tostand for 12 hours. About 81 grams of thorium oxalate, equivalent to46.2 grams of thorium, were produced.

Step 3.The acid-insoluble residue from step 2, weighing about 230 grams,was mixed with 200 grams of flake sodium hydroxide and suficient waterwas added to give a volume of about 400 milliliters. The resultingsolution was then boiled for four hours, diluted with water to 1 to 2liters and then filtered. The filtrate was discarded and the residue wastreated with 500 milliliters of 6- normal hydrochloric acid.

The insoluble residue was then mixed with about 50 grams of flake sodiumhydroxide and water was added to a volume of about 100 milliliters. Theresulting solution was boiled for about four hours, diluted to 250-500milliliters, and filtered. The filtrate was discarded and the residuewas treated with 200 milliliters of 6-normal hydrochloric acid.

The two hydrochloric acid solutions were combined and the combinedsolution was made 1 to 3 normal in hydrochloric acid. About 5milliliters of concentrated nitric acid were then added followed by 12grams of oxalic acid which precipitated the thorium as thorium oxalate.This was equivalent to about 8.8 grams of thorium.

The total recovery of thorium from step 2 and step 3 was equivalent toabout 55 grams.

The final residue from the second part of step 3 weighed about 37 grams.Thorium contained in it was recovered by dissolution in 60 percentperchloric acid followed by the addition of 12 grams of oxalic acidwhich precipitated the thorium as thorium oxalate. An additional 8.6grams of thorium were then recovered. The cost and unavailability oflarge quantities of perchloric acid make this final treatmentunattractive from a commercial point of vrew.

The thorium oxalate obtained by this process may be converted to thoriumtetrafluoride and the latter salt may then be used for the production ofthorium metal.

The foregoing illustration and embodiment of this invention are notintended to limit its scope, which is to be limited entirely by theappended claims.

What is claimed is:

1. A process for recovering thorium from a mixture containing metallicthorium, thorium hydroxide, thorium oxide, thorium tetrafiuoride andwater and acid-soluble impurities, which comprises separatingwater-soluble impurities from said mixture by water leaching, treatingthe leached material with concentrated hydrochloric acid to dissolvemetallic thorium, thorium hydroxide and acidsoluble impurities,subjecting the acid-treated residue to the action of caustic alkaliwhereby thorium oxide and thorium tetrafluoride are transformed toacid-soluble cornpounds; subjecting thecaustic-treated material to theaction ofaqneous hydrochloric acid'todissolve-the-residual thorium, andprecipitating thorium oxalate from the hydrochloric acid solutions thus,obtained. 2. A- methodofrecovering thorium comprisingdea'cw ing a,composition containing thorium with water; rernovingthe 'water solution;treating the "residu'e'witll' hydrochloric acid, separating the solutionfrom the-insoluble residue, adjusting its-acidity to 1-3 normal, addingoxalic acid; and thereafter; separatinggtheithorium oxalatethusgprecipitated, digesting; the:.-residue :from the hydrochlorie, acidtreatment with: a strong-,solutionuof sodium hydroxide 'ataan elevated:temperature; removing gsaid solution and ;treating theqinsolubleresidue; with hydrochloric acid, separating the solutionfrom-thevinsoluble residue, adjustingthe acidity; ofi the:solution to.17-3 :norma'l, adding oxalic 'acid,., and thereafter *separatingmhethorium 4 oxalate thus;,precipitated.

3. A method of separating thorium from impurities found-ina-slagcontaining thorium and" said impurities comprising leaching acomposition containing thorium with water, removing the water solution,treating the residue with hydrochloric acid, separating the solutionfrom the insoluble residue, adjusting its acidity to 1-3 normal, addingnitric acid, addingoxalic acid, and thereafter separatingthethoriumoxalate,- thus precipitated; digesting the residue from thehydrochloric acid treatment with a strongsolution of sodiumhydroxide atanelevated temperature, removing said solution and treating theinsoluble residue with hydrochloric acid, separating the solution fromthe'ainsoluble'residue, adjusting the: acidity of this solution to 1-3normal, addingtnitric acid to oxidize the iron present, adding oxalicacid and thereafter separating the thorium oxalate thus precipitated.

No references cited.

1. PROCESS FOR RECOVERING THORIUM FROM A MIXTURE CONTAINING METALLICTHORIUM, THORIUM HYDROXIDE, THORIUM OXIDE, THORIUM TETRAFLUORIDE ANDWATER AND ACID-SOLUBLE IMPURITIES, WHICH COMPRISES SEPARATINGWATER-SOLUBLE IMPURITIES FROM SAID MIXTURE BY WATER LEACHING, TREATINGTHE LEACHED MATERIAL WITH CONCENTRATED HYDROOCHLORIC ACID TO DISSOLVEMETALLIC THORIUM, THORIUM HYDROXIDE AND ACIDSOLUBLE IMPURITIES,SUBJECTING THE ACID-TREATED RESIDUE TO THE ACTION OF CAUSTIC ALKALIWHEREBY THORIUM OXIDE AND THORIUM TETRAFLUORIDE ARE TRANSFORMED TOACID-SOLUBLE COMPOUNDS, SUBJECTING THE CAUSTIC-TREATED MATERIAL TO THEACTION OF AQUEOUS HYDROCHLORIC ACID TO DISSOLVE THE RESIDUAL THORIUM,AND PRECIPATING THORIUM OXALATE FROM THE HYDROCHLORIC ACID SOLUTIONSTHUS OBTAINED.